Recharge systems for protecting and enhancing groundwate

54
TOPIC 1
Recharge systems / River/lake bank filtration and pond infiltration issues
concentrations are associated with low dissolved iron concentrations. Thus, the advantage of appropriately selecting
abstraction wells covers both parameters. Since the water quality change for bank filtrate was very similar in all
wells, an improvement of raw water quality can be achieved mainly by the selection of wells abstracting the proportion
of landside groundwater with the best quality. At the Torgau waterworks, the preferential operation of these
wells has already resulted in cost savings, especially for the removal of dissolved iron during the water treatment
process that requires iron sludge disposal (Grischek, 2003b).
Another method was chosen at the Mockritz waterworks, located north of the city of Torgau. To adapt the operation
of wells to the decreasing water demand, to allow almost continuous well operation and to use the whole aquifer as
a reactor for pre-treatment, the installed pump capacity of the wells was reduced.
CONCLUSIONS
A site-specific, scientifically based and long-term monitoring of bank filtrate and groundwater quality is the basis
for an effective management of bank filtration sites and the prediction of changes in water flow and quality. The
understanding of the pattern of contaminant migration and location of biogeochemical reaction zones is a prerequisite
to an effective determination of pumping strategies to optimise the system for best quality at lowest cost. The
main aim of using river bank filtration as a pre-treatment of River Elbe water is the attenuation of organic compounds
and low concentrations of DOC. Long flow paths and retention times promote the attenuation of organics,
but were found to have only a relatively small effect on iron and manganese concentrations. From a water quality
point of view, continuous pumping of selected wells is preferred over periodic operation.
At all sites with long flow paths, mixing ratios of bank filtrate and groundwater were found to be of main importance
for the concentration of DOC, nitrate, sulfate, dissolved iron and manganese in abstracted water. Due to
spatially varying groundwater quality within the whole catchment zone, a selection of wells having a catchment
zone with good groundwater quality at the land side offered a significant improvement in raw water quality. A
detailed investigation of groundwater flow conditions and proportions of bank filtrate in the raw water is very
important for deciding effective water quality management measures. Thus, management of bank filtration schemes
should be incorporated into wider catchment planning in order to limit potentially polluting activities in the
groundwater recharge area.
REFERENCES
Grischek T. (2003a). Zur Bewirtschaftung von Uferfiltratfassungen an der Elbe (Management of bank filtration sites along
the River Elbe). PhD thesis, Department of Forestry, Geo- and Hydrosciences, Dresden University of Technology.
Grischek T. (2003b). Water quality management for existing riverbank filtration sites along the Elbe River in
Germany. In: Proc. 2nd Int. Riverbank Filtration Conf., G. Melin (ed.), 16–19 Sept. 2003, Cincinnati, USA,
pp. 63–68.
Krueger M. and Nitzsche I. (2003). The 100-year flood of the Elbe River in 2002 and its effects on riverbank
filtration sites. In: Proc. 2nd Int. Riverbank Filtration Conf., G. Melin (ed.), 16–19 Sept. 2003, Cincinnati, USA,
pp. 81–85.
Nestler W., Walther W., Jacobs F., Trettin R. and Freyer, K. (1998). Wassergewinnung in Talgrundwasserleitern im
Einzugsgebiet der Elbe (Water production in alluvial aquifers along the River Elbe). UFZ-Research Report 7, 203 p.
Nestler W., Nitzsche I. and Krüger M. (1996). Untersuchungen zur Beschaffenheit des Uferfiltrats in den Torgauer
Talgrundwasserleitern (Investigations into bank filtrate quality the Elbe River basin near Torgau). gwf Wasser-
Abwasser, 137(9), pp. 480–486.
ISMAR 2005 ■ AQUIFER RECHARGE ■ 5th International Symposium ■ 10 –16 June 2005, Berlin